HVAC systems are designed to maintain indoor air quality and provide thermal space conditioning. HVAC is important in the design of industrial and office buildings where safe and healthy building conditions are regulated with respect to temperature and humidity, using fresh air from outdoors.
Central heating is often used in cool climates to heat buildings. Central heating systems contain a boiler, furnace or heat pump to warm water, steam or air in a central location such as a furnace room in a home or a mechanical room in large buildings. These systems also contain either duct work in forced air systems or piping to distribute a heated fluid to radiators or a heat exchanger to transfer this heat to the air.
The use of water as the heat transfer medium is known as hydronics. In a hydronic heating system, water within is heated in a boiler and discharged into piping which carries it to a heat exchanger or heating coil. Air is drawn through the coil and is warmed. The water within the coil, now at a lower temperature due to the transfer of heat to the incoming or surrounding air, is returned to the boiler for reheating. Especially in cool climates, hydronic heating systems are typically installed as central heating systems within the interior of the building. Often times, however, this is undesirable due to space limitations, complexity of installation and the inability to easily retrofit new or upgraded systems into an existing building.
While certain heating systems can be deployed on the rooftop of buildings (known as packaged rooftop units), thereby providing for ease of installation/retrofitting, hydronic heating systems have typically not been used on the roof because of the need to bring water piping to the roof and concerns about operation at subfreezing temperatures.
In view of the above, there is a need for a packaged, rooftop hydronic air heater that is capable of consistent and efficient operation at subfreezing temperatures.